fix(session): Automatically detect and remove dangling tool calls whe… by liuxh613 · Pull Request #873 · agentscope-ai/agentscope-java

liuxh613 · 2026-03-05T06:42:04Z

Describe the bug
When restoring Agent state from a persistent session (such as a database), if the Memory contains incomplete tool calls (ToolUseBlock without a corresponding ToolResultBlock), it causes the following error:
java.lang.IllegalStateException: Cannot add messages without tool results when pending tool calls exist.
Pending IDs: [call_ba1efbfa083f4323adb4f9]

To Reproduce
Steps to reproduce the behavior:

You code
How to execute
See error
Expected behavior
The ReActAgent.loadFrom() method can include automatic cleanup logic.

Error messages
2026-03-05 12:22:57.040 INFO [] io.agentscope.core.tool.Toolkit Line:239 - Registered tool 'context_reload' in group 'ungrouped'
2026-03-05 12:22:57.040 INFO [] io.agentscope.core.memory.autocontext.AutoContextHook Line:185 - AutoContextMemory integration completed for agent: ReActAgent
Error during execution: Cannot add messages without tool results when pending tool calls exist. Pending IDs: [call_ba1efbfa083f4323adb4f9]
java.lang.IllegalStateException: Cannot add messages without tool results when pending tool calls exist. Pending IDs: [call_ba1efbfa083f4323adb4f9]
at io.agentscope.core.ReActAgent.validateAndAddToolResults(ReActAgent.java:335)
at io.agentscope.core.ReActAgent.doCall(ReActAgent.java:256)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:133)
at io.agentscope.core.tracing.TracerRegistry$1.lambda$onNext$0(TracerRegistry.java:92)
at io.opentelemetry.context.Context.lambda$wrapSupplier$8(Context.java:344)
at io.agentscope.core.tracing.telemetry.TelemetryTracer.runWithContext(TelemetryTracer.java:226)
at io.agentscope.core.tracing.TracerRegistry$1.onNext(TracerRegistry.java:89)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onNext(FluxHide.java:137)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:130)
at io.agentscope.core.tracing.TracerRegistry$1.lambda$onNext$0(TracerRegistry.java:92)
at io.opentelemetry.context.Context.lambda$wrapSupplier$8(Context.java:344)
at io.agentscope.core.tracing.telemetry.TelemetryTracer.runWithContext(TelemetryTracer.java:226)
at io.agentscope.core.tracing.TracerRegistry$1.onNext(TracerRegistry.java:89)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onNext(FluxHide.java:137)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondComplete(MonoFlatMap.java:246)
at reactor.core.publisher.MonoFlatMap$FlatMapInner.onNext(MonoFlatMap.java:307)
at io.agentscope.core.tracing.TracerRegistry$1.lambda$onNext$0(TracerRegistry.java:92)
at io.opentelemetry.context.Context.lambda$wrapSupplier$8(Context.java:344)
at io.agentscope.core.tracing.telemetry.TelemetryTracer.runWithContext(TelemetryTracer.java:226)
at io.agentscope.core.tracing.TracerRegistry$1.onNext(TracerRegistry.java:89)
at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
at reactor.core.publisher.MonoFlatMap$FlatMapInner.onSubscribe(MonoFlatMap.java:293)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:56)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:166)
at io.agentscope.core.tracing.TracerRegistry$1.lambda$onNext$0(TracerRegistry.java:92)
at io.opentelemetry.context.Context.lambda$wrapSupplier$8(Context.java:344)
at io.agentscope.core.tracing.telemetry.TelemetryTracer.runWithContext(TelemetryTracer.java:226)
at io.agentscope.core.tracing.TracerRegistry$1.onNext(TracerRegistry.java:89)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onNext(FluxHide.java:137)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondComplete(MonoFlatMap.java:246)
at reactor.core.publisher.MonoFlatMap$FlatMapInner.onNext(MonoFlatMap.java:307)
at io.agentscope.core.tracing.TracerRegistry$1.lambda$onNext$0(TracerRegistry.java:92)
at io.opentelemetry.context.Context.lambda$wrapSupplier$8(Context.java:344)
at io.agentscope.core.tracing.telemetry.TelemetryTracer.runWithContext(TelemetryTracer.java:226)
at io.agentscope.core.tracing.TracerRegistry$1.onNext(TracerRegistry.java:89)
at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
at reactor.core.publisher.MonoFlatMap$FlatMapInner.onSubscribe(MonoFlatMap.java:293)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:56)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:166)
at io.agentscope.core.tracing.TracerRegistry$1.lambda$onNext$0(TracerRegistry.java:92)
at io.opentelemetry.context.Context.lambda$wrapSupplier$8(Context.java:344)
at io.agentscope.core.tracing.telemetry.TelemetryTracer.runWithContext(TelemetryTracer.java:226)
at io.agentscope.core.tracing.TracerRegistry$1.onNext(TracerRegistry.java:89)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onNext(FluxHide.java:137)
at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.request(FluxHide.java:152)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:195)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.request(FluxHide.java:152)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:195)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.request(FluxHide.java:152)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:172)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.request(FluxHide.java:152)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:195)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.request(FluxHide.java:152)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:195)
at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:2361)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onSubscribe(FluxOnErrorResume.java:75)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:118)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onSubscribe(FluxHide.java:123)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:118)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onSubscribe(FluxHide.java:123)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:96)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onSubscribe(FluxHide.java:123)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:118)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onSubscribe(FluxHide.java:123)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:118)
at io.agentscope.core.tracing.TracerRegistry$1.onSubscribe(TracerRegistry.java:83)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onSubscribe(FluxHide.java:123)
at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:56)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:56)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
at reactor.core.publisher.MonoUsing.subscribe(MonoUsing.java:109)
at reactor.core.publisher.Mono.subscribe(Mono.java:4569)
at reactor.core.publisher.Mono.block(Mono.java:1772)
at io.agentscope.examples.advanced.DaMengRAGFlowStudioExample.main(DaMengRAGFlowStudioExample.java:318)
Suppressed: java.lang.Exception: #block terminated with an error
at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104)
at reactor.core.publisher.Mono.block(Mono.java:1773)
... 1 more

Saving final session...
Closing resources...
2026-03-05 12:22:57.116 INFO [] com.zaxxer.hikari.HikariDataSource Line:349 - HikariPool-1 - Shutdown initiated...
2026-03-05 12:22:57.118 INFO [] com.zaxxer.hikari.HikariDataSource Line:351 - HikariPool-1 - Shutdown completed.
Shutting down Studio...
✓ Done

2026-03-05 12:22:57.120 INFO [] io.agentscope.core.studio.StudioWebSocketClient Line:154 - Socket.IO disconnected from /python namespace
2026-03-05 12:23:57.137 INFO [] io.agentscope.core.model.transport.HttpTransportFactory Line:185 - Shutting down 1 managed HttpTransport(s)

Environment (please complete the following information):

AgentScope-Java Version: 1.0.10-SNAPSHOT
Java Version: 21
OS: windows11
Additional context
Add any other context about the problem here.

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Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...e/src/main/java/io/agentscope/core/ReActAgent.java	81.81%	0 Missing and 2 partials ⚠️

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gemini-code-assist · 2026-03-05T07:39:49Z

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Copilot

Pull request overview

Fixes session restoration failures for ReActAgent when persisted memory contains incomplete (dangling) tool calls, preventing IllegalStateException on the next user interaction.

Changes:

Add automatic cleanup on ReActAgent.loadFrom() to remove dangling tool-call state after restoring memory.
Add unit tests covering cleanup behavior and non-cleanup behavior on restore.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
agentscope-core/src/main/java/io/agentscope/core/ReActAgent.java	Runs cleanup after memory restoration to avoid pending-tool-call illegal state.
agentscope-core/src/test/java/io/agentscope/core/agent/ReActAgentTest.java	Adds tests for cleanup of pending tool calls across session restore scenarios.

agentscope-core/src/test/java/io/agentscope/core/agent/ReActAgentTest.java

+        Msg toolResultMsg =
+                Msg.builder()
+                        .name("User")
+                        .role(MsgRole.USER)
+                        .content(
+                                List.of(
+                                        ToolResultBlock.builder()
+                                                .id("call_complete_456")
+                                                .output(
+                                                        List.of(
+                                                                TextBlock.builder()
+                                                                        .text("Sunny, 25°C")
+                                                                        .build()))
+                                                .build()))
+                        .build();
+        memory.addMessage(toolResultMsg);


agentscope-core/src/main/java/io/agentscope/core/ReActAgent.java

+     * session. This method removes the last assistant message if it contains tool calls without
+     * corresponding results, preventing IllegalStateException on the next user input.
+     */
+    private void cleanupPendingToolCalls() {
+        Set<String> pendingIds = getPendingToolUseIds();
+        if (!pendingIds.isEmpty()) {
+            // Find and remove the last assistant message with pending tool calls
+            List<Msg> messages = memory.getMessages();
+            for (int i = messages.size() - 1; i >= 0; i--) {
+                Msg msg = messages.get(i);
+                if (msg.getRole() == MsgRole.ASSISTANT) {
+                    memory.deleteMessage(i);
+                    log.warn(
+                            "Removed incomplete tool calls from restored session. Pending IDs: {}",
+                            pendingIds);
+                    break;
+                }
+            }


LearningGp · 2026-03-18T08:20:45Z

agentscope-core/src/main/java/io/agentscope/core/ReActAgent.java

+        Set<String> pendingIds = getPendingToolUseIds();
+        if (!pendingIds.isEmpty()) {
+            // Find and remove the last assistant message with pending tool calls
+            List<Msg> messages = memory.getMessages();


getMessages() returns a filtered copy; indices might be out of sync with the internal list.

LearningGp · 2026-03-18T08:23:31Z

In my view, storing unexpected messages in the session shouldn't be handled at the framework level; instead, they should be surfaced to the developer. This might warrant further discussion.

LearningGp · 2026-03-24T03:05:51Z

FYI (#956)

liuxh613 · 2026-03-24T06:33:24Z

FYI (#956)

thanks，This seems like a solution approach.

fix(session): Automatically detect and remove dangling tool calls whe…

ee96e85

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liuxh613 requested a review from a team March 5, 2026 06:42

liuxh613 mentioned this pull request Mar 5, 2026

[Bug]: java.lang.IllegalStateException: Cannot add messages without tool results when pending tool calls exist. #871

Open

liuxh613 force-pushed the session_restoration branch from 857e491 to ee96e85 Compare March 5, 2026 07:22

liuxh613 marked this pull request as draft March 5, 2026 07:39

liuxh613 marked this pull request as ready for review March 5, 2026 07:39

ci: add ut

dd21b04

LearningGp requested a review from Copilot March 18, 2026 08:07

Copilot started reviewing on behalf of LearningGp March 18, 2026 08:07 View session

Copilot AI reviewed Mar 18, 2026

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LearningGp requested changes Mar 18, 2026

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LearningGp added the wait-for-response PRs that require further response label Mar 23, 2026

liuxh613 closed this Mar 24, 2026

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